Assembly for positioning a sterile surgical drape relative to optical position sensors

ABSTRACT

A camera and drape assembly for use with tracking elements of a surgical system includes a camera unit and a drape covering the camera unit. The camera unit includes a casing presenting a face for facing the tracking elements. Optical sensors are supported by the casing and are exposed through the casing for detecting the tracking elements. The drape covers the camera unit such that light signals from the tracking elements can be received by the optical sensors.

RELATED APPLICATIONS

This application claims priority to and all the benefits of U.S.Provisional Patent Application No. 61/788,752 which was filed on Mar.15, 2013, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention generally relates to a camera and drape assemblyfor an operating room. Specifically, the camera and drape assemblyincludes a camera unit having an optical sensor and a surgical drape forseparating the camera unit from a sterile field of the operating room.

BACKGROUND

A sterile drape is used in some operating rooms to separate a sterilefield for a surgical procedure. For example, some operating roomsinclude a guidance station that tracks movement of various objects inthe operating room. Such objects include, for example, a surgicalinstrument and anatomy of the patient. The guidance station tracks theseobjects for purposes of displaying their relative positions andorientations to the surgeon and, in some cases, for purposes ofcontrolling or constraining movement of the surgical instrument relativeto a predefined path or anatomical boundary. Many components of theguidance station cannot be adequately and/or easily sterilized. As such,a sterile drape is used to separate at least some of the components ofthe guidance station from the sterile field.

The guidance station includes a localizer that includes a camera unit.The camera unit includes optical sensors, e.g., charge-coupled devices(CCD), for tracking the objects in the operating room. Specifically, thecamera unit tracks the position of tracking devices fixed to objects inthe operating room such as surgical instruments and anatomy of thepatient. The optical sensors of the localizer receive light signalsemitted from the tracking devices, e.g., with the use of light emittingdiodes (LEDs) fixed to the tracking devices. Based on the positions ofthe tracking devices, the guidance station calculates the positionand/or orientation of the surgical instrument and the anatomy of thepatient.

An unobstructed view is sought between the optical sensors of the cameraunit and the tracking devices so that the optical sensors can accuratelydetect the light signals transmitted by the tracking devices. Thetracking devices are in the sterile field on the surgical instrumentsand on the anatomy of the patient. The camera unit cannot be adequatelyand/or easily sterilized, so the sterile drape separates the camera unitfrom the sterile field of the operating room and, thus, separates thecamera unit from the tracking devices.

The sterile drape can interfere with proper light detection by thecamera unit. For example, wrinkles in the sterile drape between theoptical sensors and the tracking devices interfere with the ability ofthe optical sensors to adequately detect the tracking devices. Asanother example, if the drape extends at a transverse plane relative tothe optical sensors, i.e., is not co-planar with the optical sensors,the drape can distort the light detection of the camera unit. As such,there remains an opportunity to provide an adequate view between theoptical sensors of the camera unit outside of the sterile field and thetracking devices inside the sterile field so that the optical sensorscan accurately detect the tracking devices.

SUMMARY

One embodiment provides a camera and drape assembly for use with atracking element of a surgical system. A camera unit includes a casing.The camera unit further includes an optical sensor supported by thecasing for detecting the tracking element. A drape includes a firstsection having a first elasticity and a second section surrounded by thefirst section and having a second elasticity greater than the firstelasticity. The casing presents a lip with the second section extendingaround and elastically engaging the lip for supporting the drape overthe optical sensor.

One advantage of this embodiment is that the lip supports the drape andpositions the drape relative to the optical sensor to provide anunobstructed view between the optical sensor and the tracking element sothat the optical sensor can accurately detect the tracking element. Forexample, the camera unit positions the drape in front of the opticalsensors free of wrinkles that could interfere with proper detection bythe optical sensor. As another example, the camera unit positions thedrape in front of the optical sensor in substantially coplanar positionrelative to the optical sensor. As such, the camera unit allows forunobstructed line-of-sight between the optical sensor and the trackingelement.

In another embodiment a camera and drape assembly is provided for usewith a tracking element of a surgical system. A camera unit includes acasing. The camera unit further includes an optical sensor supported bythe casing for detecting the tracking element. A drape includes aflexible section and a window that is rigid relative to the flexiblesection. The window is surrounded by the flexible section. The cameraunit includes a first coupling device. The drape includes a secondcoupling device that mates with the first coupling device to align thewindow with the optical sensor.

One advantage of this embodiment is that the relatively rigid windowprovides a wrinkle-free, transparent sterile barrier between the cameraunit and the tracking element that enables light signals from thetracking element to be properly received by the optical sensor.Additionally, the coupling devices further provide appropriatepositioning of the drape on the camera unit to maintain alignmentbetween the window and the optical sensor.

In another embodiment a camera and drape assembly is provided for usewith a tracking element of a surgical system. The camera unit includes acasing having a base and a post extending upwardly from the base. Thecamera unit further includes a plurality of optical sensors supported bythe casing for detecting the tracking element. A drape has a flexiblesection for draping over the post of the casing to cover the casing andthe optical sensors. A collar is sized for fitting over the post to trapthe flexible section of the drape between the collar and the post.

One advantage of this embodiment is that the collar is able to placetension on the flexible section across the casing to remove wrinkles andprovide a wrinkle-free, transparent sterile barrier between the cameraunit and the tracking element that enables light signals from thetracking element to be properly received by the optical sensors.

In another embodiment a drape is provided for use with a camera unithaving a casing, an optical sensor supported by the casing, and a lip.The drape comprises a first section having a first elasticity and asecond section surrounded by the first section and having a secondelasticity greater than the first elasticity. The second section isconfigured to extend around and elastically engaging the lip of thecamera unit for supporting the drape over the optical sensor.

In yet another embodiment, a drape is provided for use with a cameraunit having a casing, an optical sensor supported by the casing, and afirst coupling device. The drape comprises a flexible section and awindow that is rigid relative to the flexible section and surrounded bythe flexible section. The drape includes a second coupling deviceconfigured to mate with the first coupling device to align the windowover the optical sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a perspective view of a guidance station including a cameraassembly in an operating room;

FIG. 2 is a partially exploded view of a first embodiment of the cameraassembly including a camera unit and a drape;

FIG. 3 is a perspective view of the camera assembly of FIG. 2 with thedrape assembled to the camera unit;

FIG. 4A is a cross-section view of a portion of the camera assemblytaken along line 4A of FIG. 2;

FIG. 4B is a cross-section view of a portion of the camera assemblytaken along line 4B of FIG. 3;

FIG. 5 is a partially exploded view of a second embodiment of the cameraassembly including a camera unit and a drape;

FIG. 6 is a perspective view of the camera assembly of FIG. 5 with thedrape assembled to the camera unit;

FIG. 7 is a partially exploded view of a third embodiment of the cameraassembly including a camera unit and a drape;

FIG. 8 is a perspective view of the camera assembly of FIG. 7 with thedrape assembled to the camera unit;

FIG. 9 is a partially exploded view of a fourth embodiment of the cameraassembly including a camera unit and a drape;

FIG. 10 is a perspective view of the camera assembly of FIG. 9 with thedrape assembled to the camera unit;

FIG. 10A is a partial cross-sectional view taken generally along line10A in FIG. 10;

FIG. 11 is a partially exploded view of a fifth embodiment of the cameraassembly including a camera unit and a drape;

FIG. 12 is a perspective view of the camera assembly of FIG. 11 with thedrape assembled to the camera unit;

FIG. 12A is a partial cross-sectional view taken generally along line12A in FIG. 12;

FIG. 13 is a partially exploded view of a sixth embodiment of the cameraassembly including a camera unit and a drape;

FIG. 14 is a perspective view of the camera assembly of FIG. 13 with thedrape assembled to the camera unit;

FIG. 15 is a partially exploded view of a seventh embodiment of thecamera assembly including a camera unit and a drape;

FIG. 16 is a perspective view of the camera assembly of FIG. 15 with thedrape assembled to the camera unit;

FIG. 17 is a partially exploded view of a eighth embodiment of thecamera assembly including a camera unit and a drape;

FIG. 18 is a perspective view of the camera assembly of FIG. 17 with thedrape assembled to the camera unit;

FIG. 18A is a partial cross-sectional view illustrating an abutment andelastic band;

FIG. 19 is a partially exploded view of a ninth embodiment of the cameraassembly including a camera unit and a drape;

FIG. 20 is a perspective view of the camera assembly of FIG. 19 with thedrape assembled to the camera unit;

FIG. 21 is a partially exploded view of a tenth embodiment of the cameraassembly including a camera unit and a drape;

FIG. 22 is a perspective view of the camera assembly of FIG. 21 with thedrape assembled to the camera unit;

FIG. 22A is a partial cross-sectional view taken generally along line22A in FIG. 22;

FIG. 23 is a partially exploded view of a eleventh embodiment of thecamera assembly including a camera unit and a drape;

FIG. 24 is a perspective view of the camera assembly of FIG. 23 with thedrape assembled to the camera unit;

FIG. 24A is a partial cross-sectional view taken generally along line24A in FIG. 24;

FIG. 25 is a partially exploded view of a twelfth embodiment of thecamera assembly including a camera unit and a drape;

FIG. 26 is a perspective view of the camera assembly of FIG. 25 with thedrape assembled to the camera unit;

FIG. 26A is a partial cross-sectional view taken generally along line26A in FIG. 26;

FIG. 27 is a partially exploded view of a thirteenth embodiment of thecamera assembly including a camera unit and a drape; and

FIG. 28 is a perspective view of the camera assembly of FIG. 27 with thedrape assembled to the camera unit.

DETAILED DESCRIPTION

With reference to FIG. 1, a surgical system includes a guidance station20 and tracking devices associated with various objects. The trackingdevices, e.g., trackers 44, 46, 48 discussed further below, are capableof communicating with the guidance station 20 to track the objects.

In FIG. 1, the guidance station 20 is shown in an operating room of amedical facility. A sterile drape, such as those described in thevarious embodiments below, separates a sterile field of the operatingroom. The guidance station 20 is set up to track movement of the variousobjects in the operating room. Such objects include, for example, asurgical instrument 22, a femur F, and a tibia T. The guidance station20 tracks these objects for purposes of displaying their relativepositions and orientations to the surgeon and, in some cases, forpurposes of controlling or constraining movement of the surgicalinstrument 22 relative to a predefined path or anatomical boundary.

The guidance station 20 includes a computer cart assembly 24 that housesa navigation computer 26, or other type of control unit that includesone or more processors (not numbered). A navigation interface is inoperative communication with the navigation computer 26. The navigationinterface includes a first display 28 adapted to be situated outside ofthe sterile field and a second display 29 adapted to be situated insidethe sterile field.

A camera assembly 34, also referred to as a localizer 34, communicateswith the navigation computer 26. The camera assembly 34 tracks trackingelements of the surgical system. In the embodiment shown, the cameraassembly 34 includes a camera unit 36, also referred to as a sensingdevice 36. The camera unit 36 also includes optical sensors 40 supportedby the casing 38 and exposed through the casing 38 for detecting thetracking elements.

Referring to FIG. 2, the camera unit 36 includes a casing 38 presentinga face 39 for facing the tracking elements, which in the disclosedembodiments are active or passive markers. Several embodiments of thecasing are set forth below. In some embodiments at least two opticalsensors 40 are employed. For example, as shown in several of theFigures, four optical sensors 40 are employed. The optical sensors 40may be separate charge-coupled devices (CCD). It should be appreciatedthat in other embodiments, separate camera units, each with a separateCCD, or two or more CCDs, could also be arranged around the operatingroom. The optical sensors 40 detect infrared (IR) signals.

Camera unit 36 is mounted on an adjustable arm to position the opticalsensors 40 with a field of view of the tracking elements that, ideally,is free from obstructions. The adjustable arm allows adjustment of thecamera unit 36 in at least one degree of freedom and, in someembodiments, in two or more degrees of freedom.

With reference back to FIG. 1, the camera unit 36 includes a cameracontroller 42 (internal to casing 38) in communication with the opticalsensors 40 to receive signals from the optical sensors 40. The cameracontroller 42 communicates with the navigation computer 26 througheither a wired or wireless connection (not shown). Position andorientation signals and/or data are transmitted to the navigationcomputer 26 for purposes of tracking the objects. The displays 28, 29and camera unit 36 may be like those described in U.S. Pat. No.7,725,162 to Malackowski, et al. issued on May 25, 2010, entitled“Surgery System”, hereby incorporated by reference.

Guidance station 20 communicates with the tracking elements on thetracking devices 44, 46, 48, also referred to herein as trackers. In theillustrated embodiment, one tracker 44 is firmly affixed to the femur Fof the patient and another tracker 46 is firmly affixed to the tibia Tof the patient. Trackers 44, 46 are firmly affixed to sections of bone.Trackers 44, 46 may be attached to the femur F and tibia T in the mannershown in U.S. Pat. No. 7,725,162, hereby incorporated by reference.Trackers 44, 46 could also be mounted like those shown in U.S.Provisional Patent Application No. 61/753,219, filed on Jan. 16, 2013,entitled, “Tracking Devices and Navigation Systems and Methods for UseThereof”, herein incorporated by reference. In additional embodiments, atracker is attached to the patella (not shown) to track a position andorientation of the patella. In yet further embodiments, the trackers 44,46 could be mounted to other tissue types or parts of the anatomy.

An instrument tracker 48 is rigidly attached to the surgical instrument22. The instrument tracker 48 may be integrated into the surgicalinstrument 22 during manufacture or may be separately mounted to thesurgical instrument 22 in preparation for the surgical procedure. Theworking end of the surgical instrument 22, which is being tracked byvirtue of the instrument tracker 48, may be a rotating bur, electricalablation device, or the like.

In the embodiment shown in FIG. 1, the surgical instrument 22 is an endeffector of a machining station 56. Such an arrangement is shown in U.S.Provisional Patent Application No. 61/679,258, entitled, “SurgicalManipulator Capable of Controlling a Surgical Instrument in either aSemi-Autonomous Mode or a Manual, Boundary Constrained Mode”, thedisclosure of which is hereby incorporated by reference.

The optical sensors 40 of the camera assembly 34 receive light signalsfrom the tracking elements of the trackers 44, 46, 48. In theillustrated embodiment, the trackers 44, 46, 48 are active trackers. Inthis embodiment, each tracker 44, 46, 48 has at least three activemarkers for transmitting light signals to the optical sensors 40. Theactive markers can be, for example, light emitting diodes or LEDs 50transmitting light, such as infrared light. The optical sensors 40preferably have sampling rates of 100 Hz or more, more preferably 300 Hzor more, and most preferably 500 Hz or more. In some embodiments, theoptical sensors 40 have sampling rates of 8000 Hz. The sampling rate isthe rate at which the optical sensors 40 receive light signals fromsequentially fired LEDs 50. In some embodiments, the light signals fromthe LEDs 50 are fired at different rates for each tracker 44, 46, 48.

In other embodiments, the trackers 44, 46, 48 may have passive markers(not shown), such as reflectors that reflect and transmit light emittedfrom the camera unit 36. The reflected light is then received by theoptical sensors 40. Tracking elements such as the above described activeand passive markers are well known in the art.

Based on the positions of the LEDs 50 and previously loaded datarelating to the patient's anatomy and the surgical instrument 22,navigation computer 26 determines the position and orientation of thesurgical instrument 22 relative to the tissue (e.g., femur F and tibiaT) against which the working end is to be applied. The previously loadeddata includes data associated with pre-operative images, including MRIimages, CT scans, etc. taken before the surgical procedure. Thepreviously loaded data also includes geometric relationships between theworking end of the surgical instrument 22 and the LEDs 50 on instrumenttracker 48. Using navigation techniques for registration and coordinatesystem transformation, the patient's anatomy and the working end of thesurgical instrument 22 can be registered into a coordinate referenceframe of the localizer 34 so that the working end and the anatomy can betracked together using the LEDs 50.

In some embodiments, navigation computer 26 forwards position and/ororientation data to a manipulator controller 54. The manipulatorcontroller 54 can then use the data to control the machining station 56as described in U.S. patent application Ser. No. 13/958,070, filed onAug. 2, 2013, entitled, “Surgical Manipulator Capable of Controlling aSurgical Instrument in Multiple Modes,” the disclosure of which ishereby incorporated by reference.

The navigation computer 26 also generates image signals that indicatethe relative position of the surgical instrument working end to thesurgical site. These image signals are applied to the displays 28, 29.Displays 28, 29, based on these signals, generate images that allow thesurgeon and surgical personnel to view the relative position of thesurgical instrument working end to the surgical site. The displays, 28,29, as discussed above, may include a touch screen or other input/outputdevice that allows entry of commands.

A sterile drape separates the guidance system 20 from the sterile field.The sterile drape is removeably engaged with the camera unit 36. Thedrape is typically formed of high-density polyethylene (HDPE) orlow-density polyethylene (LDPE).

Several embodiments of camera and drape assemblies are set forth furtherbelow. If not properly arranged in front of the optical sensors 40, thedrape can interfere with proper light detection by the optical sensors40. For example, wrinkles in the drape in front of the optical sensors40 or an offset inclination of the drape relative to the optical sensors40 can interfere with proper light detection by the optical positioningsensors 40.

A first embodiment of a camera and drape assembly 100 is shown in FIGS.2-4 b. The assembly 100 includes a drape 102 and the camera unit 36. Thedrape 102 includes a first section 104 and a plurality of secondsections 106 surrounded by the first section 104. The first section 104has a first elasticity and the second sections 106 each have a secondelasticity greater than the first elasticity, making the second sections106 more elastic than the first section 104 and capable of greaterstretching than the first section 104.

With reference to FIG. 4a , the second sections 106 are thin relative tothe first section 104. In such a configuration, the second sections 106can be formed of the same material as the first section 104 and therelative thickness of the second sections 106 provides the secondsections 106 with the second elasticity greater than the firstelasticity. Alternatively, the first section 104 can be formed of afirst material and the second sections 106 can be formed of a secondmaterial different than the first material and having greater elasticitythan the first material. In such a configuration, the thickness of thesecond sections 106 can be similar to or different than the thickness ofthe first section 104.

As one example, the drape 102 may contain two or more second sections106 with each second section 106 being surrounded by the first section104. As shown in FIG. 2, the drape 102 includes four second sections106. Specifically, the drape 102 includes one second section 106associated with each optical sensor 40 and each second section 106 isdisposed between the optical sensor 40 and at least one of the trackers44, 46, 48.

The second sections 106 are integrated with the first section 104, i.e.the first section 104 and the second sections 106 are a one-piece unit.For example, the first section 104 and the second sections 106 can beformed together simultaneously as a unit or can be formed separately andsubsequently assembled and fixed together. The second sections 106 areclear or transparent to allow light to pass through without obstruction.The second sections 106 are shown circular in shape, but other shapesare contemplated.

With reference to FIGS. 2-4B, the camera unit 36 includes a lip 108spaced from the face 39 of the casing 38. A support member 41 extendsfrom the face 39 of the casing 38 to the lip 108. The support member 41extends circumferentially about one of the optical position sensors 40.The lip 108 extends circumferentially about the support member 41. Thelip 108 is annular, as shown in FIGS. 2 and 3. The support member 41 isalso annular. However, the lip 108 and the support member 41 can be ofany suitable shape without departing from the nature of this embodiment.

The camera unit 36 includes a plurality of lips 108 and support members41 with each lip 108 and support member 41 corresponding with oneoptical sensor 40. In other words, the camera unit 36 may include two ormore lips 108.

With reference to FIGS. 4A-B, each of the second sections 106 align withone of the lips 108, as shown in FIG. 4A, and is stretched over the lip108, as shown in FIG. 4B. When disassembled from each other, and withthe second section 106 in its normal state, the lip 108 has a firstdiameter D1 and the second section 106 has a second diameter D2. Thesecond diameter D2 is less than the first diameter D1 of the lip 108, asshown in FIG. 4A. In some cases, D2 is approximately the same diameteras an outer diameter of the support member 41.

The second section 106 is stretched over the lip 108 and retained on thelip 108, as shown in FIG. 4B. Retention is furthered by the firstsection 104 being stretchable over the lip 108, but having lesserelasticity and thereby constraining the second section 106 in positionover the lip 108. The second section 106 is configured to stretchuniformly across the lip 108 such that wrinkles do not develop in thesecond section 106. For example, the annular shape of the lip 108 shownin FIGS. 2 and 3 encourage uniform stretching. The drape 102 is removedfrom the camera unit 36 by pulling the drape 102 to separate the secondsections 106 from the lips 108.

The engagement of the second sections 106 on the lip 108 provides visualconfirmation that the drape 102 is properly positioned relative to thecamera unit 36 and associated optical sensors 40. Specifically, thevisual difference in thickness of the second sections 106 in comparisonto the first section 104 indicates proper positioning of the secondsections 106 relative to the camera unit 36.

The drape 102 can also include visual indicator elements 109 to aid inalignment of the stretchable second sections 106 relative to the cameraunit 36. For example, the visual indicator elements 109 can be coloredrings that encircle the second sections 106. The colored rings, such asrings of colored ink applied to the drape 102 could be located either atthe boundary between the first section 104 and the second sections 106or close thereto.

With reference to FIGS. 5 and 6, a second embodiment of a camera anddrape assembly 200 positions a drape 202 on a casing 238 of the cameraunit 236. The drape 202 includes a first flexible section 203 and asecond flexible section 205 surrounded by the first section 203. In oneversion, the first section 203 has a first elasticity and the secondsection 205 has a second elasticity greater than the first elasticity,making the second section 205 more elastic than the first section 203and capable of greater stretching than the first section 203. In theversion shown, the first and second sections 203, 205 have the sameelasticity.

An elastic band 204 is attached to the first section 203 about thesecond section 205 to position the drape 202 on the camera unit 236 andto retain the drape 202 on the camera unit 236. Specifically, the outercasing 238 of the camera unit 236 defines a lip 206 extendingcircumferentially about the camera unit 236 and the elastic band 204 isconfigured to elastically hold the second section 205 when stretchedover the lip 206. The elastic band 204 can be attached to the firstsection 203 in any fashion, such as, for example, adhesive, bonding,etc. In this embodiment, the lip 206 and elastic band 204 act as firstand second coupling devices for coupling the drape 202 to the cameraunit 236.

The first and second sections 203, 205 of the drape 202 are formed ofthin, highly flexible, transparent film or foil such as polyethylene(PE) film. The first section 203 has a constant transparency andthickness. The second section 205 has a constant transparency andthickness. The second section 205 may be thinner than the first section203 to make the second section 205 more elastic or may be of generallythe same thickness. Alternatively, the second section 205 could includeportions of different transparency and thickness than the first section203, e.g., relatively clear and thin, in an area that covers the cameraunit 236.

The engagement of the elastic band 204 on the lip 206 provides visualconfirmation that the drape 202 is properly positioned relative to thecamera unit 236. The engagement of the elastic band 204 on the lip 206can smooth the second section 205 of the drape 202 across the casing 238and/or stretches the second section 205 of the drape 202 across thecasing 238, which can thin the drape 202 in the area in front of theoptical position sensors 40 and reduce potential interference withproper light detection by the optical position sensors 40.

With reference to FIGS. 7 and 8, a third embodiment of a camera anddrape assembly 300 positions a drape 302 on an outer casing 338 of thecamera unit 336. The drape 302 includes a first flexible section 303 anda second flexible section 305 surrounded by the first section 303. Inone version, the first section 303 has a first elasticity and the secondsection 305 has a second elasticity greater than the first elasticity,making the second section 305 more elastic than the first section 303and capable of greater stretching than the first section 303. In theversion shown, the first and second sections 303, 305 have the sameelasticity.

The drape 302 also includes a rigid section 310. The rigid section 310provides a window through which light emitted by the tracking elementscan be received by the optical sensors 40.

An elastic band 304 is attached to the first section 303 to position thedrape 302 on the camera unit 336. Specifically, the outer casing 338 ofthe camera unit 336 defines a lip 306 extending circumferentially aboutthe camera unit 336 and the elastic band 304 is configured toelastically engage the lip 306. In this embodiment, the lip 306 andelastic band 304 act as first and second coupling devices for couplingthe drape 302 to the camera unit 336.

The second section 305 separates the elastic band 304 from the rigidsection 310. When attached to the camera unit 336, the rigid section 310is located in front of the optical position sensors 40. In oneembodiment, the elastic band 304 has a diameter that, in its normalstate, is less than a diameter of the rigid section 310 (see FIG. 7)thereby requiring the elastic band 304 to be stretched over the casing338.

The rigid section 310 covers the optical position sensors 40 when theelastic band 304 is engaged with the lip 306. In some cases the elasticband 304 is stretched over the entire casing 338, including the lip 306,and allowed to at least partially relax adjacent a back surface of thecasing 338. The first section 303 is also stretchable in order to enablethe elastic band 304 to stretch over the casing 338. The rigid section310 typically abuts the casing 338 when the elastic band 304 is engagedwith the lip 306.

The engagement of the elastic band 304 on the lip 306 and the placementof the rigid section 310 in front of the optical position sensors 40provide visual confirmation that the drape 202 is properly positionedrelative to the camera unit 336.

The first and second sections 303, 305 are formed of thin, highlyflexible, transparent film or foil, such as polyethylene film. The rigidsection 310 is formed of a plastic sheet that is rigid relative to thefirst and second sections 303, 305 and is transparent. The secondsection 305 defines a cutout that receives the rigid section 310. Therigid section 310 is fixed to the second section 305 in the cutout by,for example, bonding, adhesive, tape, etc.

With reference to FIGS. 9, 10, and 10A, a fourth embodiment of a cameraand drape assembly 400 positions a drape 402 on an outer casing 438 ofthe camera unit 436. A rigid collar 404 clamps the drape 402 in positionrelative to the camera unit 436. Specifically, a post 406 extends from abase of the outer casing 438 of the camera unit 436. The post 406supports the optical position sensors 40. The collar 404 is configuredto engage about the post 406 and pinch the drape 402 between the collar404 and the post 406. The collar 404 is separate from and moveablerelative to drape 402. The collar 404 may have rounded edges to preventtearing of the drape 402.

The post 406 defines an outer diameter and the collar 404 defines aninner diameter configured to receive the outer diameter of the post 406.The collar 404 is initially placed on the post 406 with the drape 402disposed therebetween, as shown in FIG. 10A, and is pressed onto thepost 406 toward the base of the outer casing 438 to stretch the drape402 across the optical position sensors 40. The collar 404 is retainedon the post 406 by a friction fit and by resting on the base.Alternatively, the collar 404 and the post 406 include engagementfeatures (not shown) for retaining the collar 404 on the post 406.

The drape 402 is formed of highly flexible, transparent film or foilsuch as polyethylene film. The drape 402 has a constant transparency andthickness. Alternatively, the drape 402 includes sections of differenttransparency and thickness, e.g., relatively clear and thin, in an areathat covers the camera unit 436. The collar 404 and the post 406, forexample, are formed of plastic or metal.

The engagement of the collar 404 on the post 406 provides visual andtactile confirmation that the drape 402 is properly positioned relativeto the camera unit 436. The collar 404 and/or the post 406 can includefeatures that provide acoustic feedback when the collar 404 is engagedwith the post 406, such as snap-lock engagement features.

With reference to FIGS. 11, 12, and 12A, a fifth embodiment of a cameraand drape assembly 500 positions a drape 502 on the outer casing 538 ofthe camera unit 536. The camera unit 536 includes first coupling devices504 fixed to and extending from the casing 538 peripherally about theoptical position sensors 40. The first coupling devices 504 aregenerally rectangular and include a first peripheral wall 505 extendingupwardly from the casing 538.

The drape 502 includes a flexible section 503 and windows 508 coupled tothe flexible section 503 through which the optical sensors 40 are ableto receive light signals from the tracking elements.

The drape 502 further includes second coupling devices 506 configured toengage the first coupling devices 504. The second coupling devices maybe generally rectangular in shape. Specifically, the first couplingdevices 504 and the second coupling devices 506 are configured to engageeach other in a friction fit or snap-fit connection.

The second coupling devices 506 each include a second peripheral wall511 that extends from the drape 502 to the window 508. The window 508 isa transparent planar section fixed to the second peripheral wall 511that is aligned with the optical position sensors 40 when the secondcoupling devices 506 are engaged with the first coupling devices 504.The windows 508 may be integrally formed with the second peripheral wall511 or may be separate (as shown) and fixed to the second peripheralwall 511 by adhesive, bonding, ultrasonic welding, or other methods.

The engagement of the second coupling devices 506 with the firstcoupling devices 504 positions the drape 502 relative to the camera unit536 and supports the drape 502 on the camera unit 536. When engaged theperipheral walls 505, 511 abut one another with the second peripheralwall 511 surrounding the first peripheral wall 505. The peripheral walls505, 511 although rigid relative to the flexible section 503 may beflexible to facilitate a friction fit therebetween. Snap-fit featuresmay also be integrated into either of the peripheral walls 505, 511 tofacilitate engagement.

The flexible section 503 of the drape 502 is formed of highly flexible,transparent film or foil such as polyethylene film. The second couplingdevices 506 and windows 508 are typically formed of a plastic that isrigid relative to the flexible section 502. The windows 508 aretransparent. The flexible section 503 defines cutouts that receive thesecond coupling devices 506. The second coupling devices 506 are fixedto the flexible section 503 in the cutouts by, for example, bonding,adhesive, tape, etc.

The engagement of the second coupling devices 506 with the firstcoupling devices 504 provides tactile confirmation that the drape 502 isproperly positioned relative to the camera unit 536. The second couplingdevices 506 may include colored borders 510 to identify the portion ofthe second coupling devices 506 that engage the first coupling devices504.

With reference to FIGS. 13 and 14, a sixth embodiment of a camera anddrape assembly 600 positions a drape 602 on an outer casing 638 of thecamera unit 636. The drape 602 includes a flexible section 603, i.e. afirst section 603, and a rigid section 610, i.e. a second section 610.The rigid section 610 is surrounded by the flexible section 603. Therigid section 610 provides a window through which light emitted by thetracking elements can be received by the optical sensors 40.

The outer casing 638 includes first coupling devices 604. In theembodiment shown the first coupling devices 604 are sockets 604. Thedrape 602 includes second coupling devices 606 for releasably couplingto the first coupling devices 604. The second coupling devices 606 areshown as plugs 606 coupled to the drape 602. The plugs 606 areconfigured to releasably fit in the sockets 604 to mount and positionthe drape 602 on the camera unit 636.

The plugs 606 are fixed to the rigid section 610, such as by adhesive,bonding, ultrasonic welding, or other methods. The rigid section 610covers the optical position sensors 40 when the plugs 606 engage andmate with the sockets 604. In FIG. 13, the plugs 606 are located beneaththe flexible section 603, but are visible in FIG. 13 since the flexiblesection 603 is transparent. In some embodiments, two, three, or moreplugs 606 are employed to prevent rotation of the drape 602 relative tothe casing 638. In other embodiments, a single plug having anon-circular geometry may be employed to prevent rotation of the drape602 relative to the casing 638.

The flexible section 603 is formed of highly flexible, transparent filmor foil such as polyethylene film. The rigid section 610 is formed of aplastic sheet that is rigid relative to the flexible section 603 and istransparent. The flexible section 603 defines a cutout that receives therigid section 610. The rigid section 610 is fixed to the flexiblesection 603 in the cutout by, for example, bonding, adhesive, tape, etc.

The coupling of the plugs 606 and sockets 604 provides visual andtactile confirmation that the drape 602 is properly positioned relativeto the camera unit 636.

With reference to FIGS. 15 and 16, a seventh embodiment of a camera anddrape assembly 700 positions a drape 702 on a casing 738 of the cameraunit 736. The drape 702 includes a flexible section 703, i.e., a firstsection 703, and rigid sections 710, i.e., second sections 710. Therigid sections 710 provide windows through which light emitted by thetracking elements can be received by the optical sensors 40.

First coupling devices 704 are fixed to the outer casing 738. The drape702 includes second coupling devices 706 for coupling to the firstcoupling devices 704. In this embodiment, the first and second couplingdevices 704, 706 are male and female parts or portions 704, 706 ofconventional snap fasteners (the male parts could be on the drape 702with the female parts on the camera unit 736 or vice versa). The snapportions 704, 706 are configured to releasably couple to each other tomount and position the drape 702 on the camera unit 736 and to supportthe drape 702 on the camera unit 736.

The rigid sections 710 cover the optical position sensors 40 when thesnap portions 704, 706 couple to each other. The second snap portions706 are fixed to the rigid section 710 of the drape 702. The first snapportions 704 are mounted and fixed to the casing 738 about the opticalsensors 40.

The flexible section 703 is formed of highly flexible, transparent filmor foil such as polyethylene film. The rigid section 710 is formed of aplastic sheet that is rigid relative to the flexible section 703 and istransparent. The flexible section 703 defines a plurality of cutoutsthat receive the rigid sections 710. The rigid sections 710 are fixed tothe flexible section 703 in the cutout by, for example, bonding,adhesive, tape, etc.

The engagement of the first and second coupling devices 704, 706provides acoustic and tactile confirmation that the drape 702 isproperly positioned relative to the camera unit 736, e.g., by snapping.

With reference to FIGS. 17, 18, and 18A, an eighth embodiment of acamera and drape assembly 800 positions a drape 802 on an outer casing838 of the camera unit 836. The drape 802 includes a flexible section803, i.e., a first section 803, and rigid sections 807, i.e., secondsections 807. The rigid sections 807 provide windows 808 through whichlight emitted by the tracking elements can be received by the opticalsensors 40. The rigid sections 807 are spaced from one another andseparated by the flexible section 803.

The rigid sections 807 are fixed to the flexible section 803. The rigidsections 807, also referred to as covers or caps, each have an upperplanar wall forming the window 808 and a peripheral wall 810. Thewindows 808 may be integrally formed with the peripheral walls 810 ormay be separate and fixed to the peripheral walls 810 by adhesive,bonding, ultrasonic welding, or other methods. The peripheral wall 810is fixed to the flexible section 803. The windows 808 are parallel witha face 839 of the casing 838.

The camera unit 836 includes first coupling devices 804. In thisembodiment, the first coupling devices 804 are retainers in the form ofclips 804 fixed to and extending from the outer casing 838. The drape802 includes a plurality of second coupling devices 806 for coupling tothe clips 804. In this embodiment, the second coupling devices 806 areflexible, elastic bands 806 configured to engage the clips 804 toposition the drape 802 relative to the camera unit 836 and to supportthe drape 802 on the camera unit 836.

Abutments 805, also known as stops or positioning elements, areconfigured to be received inside the peripheral wall 810 of the rigidsections 807 to hold the windows 808 in place as the elastic bands 806bias the rigid sections 807 against the abutments 805. The elastic bands806 encircle the peripheral walls 810 around substantially the perimeterof the peripheral walls 810 and are attached to the clips 804 whileunder tension as a result of the abutments 805 holding the rigidsections 807 in place.

The windows 808 cover the optical position sensors 40 when the elasticbands 806 are coupled to the clips 804. The peripheral walls 810 abutthe casing 838 when the elastic bands 806 are coupled to the clips 804.The rigid sections 807 may be fixed to the flexible section 803 suchthat the peripheral walls 810 extend below the flexible section 803, asshown. In this case, the elastic bands 806 engage the clips 804 beneaththe flexible section 803.

In other embodiments, the rigid sections 807 are fixed to the flexiblesection 803 such that the peripheral walls 810 extend above the flexiblesection 803. In this case, the elastic bands 806 engage the clips 804through the flexible section 803. In either case, the rigid sections 807are sized to fit over the optical position sensors 40 with the abutments805 being received within the rigid sections 807.

The engagement of the elastic bands 806 with the clips 804 providesvisual and tactile confirmation that the drape 802 is properlypositioned relative to the camera unit 836. Additionally, the abutments805 provide a tactile indication that the rigid sections 807 areabutting the abutments 805.

The flexible section 803 of the drape 802 is formed of highly flexible,transparent film or foil such as polyethylene film. The rigid sections807 are formed of a plastic that is rigid relative to the flexiblesection 803. The rigid sections 807 may be entirely transparent or onlythe windows 808 may be transparent. The flexible section 803 definescutouts that receive the rigid sections 807. The rigid sections 807 arefixed to the flexible section 803 in the cutout by, for example,bonding, adhesive, tape, etc.

With reference to FIGS. 19 and 20, a ninth embodiment of a camera anddrape assembly 900 positions a drape 902 on a casing 938 of the cameraunit 936. The drape 902 includes a flexible section 903, i.e., a firstsection 903, and rigid sections 908, i.e., second sections 908. Therigid sections 908 provide windows through which light emitted by thetracking elements can be received by the optical sensors 40. The rigidsections 908 are spaced from one another and separated by the flexiblesection 903.

The camera unit 936 includes first coupling devices 904. The drape 902includes second coupling devices 906 for coupling with the firstcoupling devices 904. In the embodiment shown the first coupling devices904 are ferromagnetic mounts 904 fixed to the casing 938 and the secondcoupling devices 906 are magnets 906 fixed to the rigid sections 908 (orthe ferromagnetic mounts 904 could be on the rigid sections 908 with themagnets 906 on the casing 938). The drape 902 is mounted to the cameraunit 936 by magnetic attraction between the ferromagnetic mounts 904 andthe magnets 906 to position the drape 902 relative to the camera unit936 and to support the drape 902 on the camera unit 936.

The rigid sections 908 cover the optical position sensors 40 when themounts 904 and magnets 906 couple to each other so that the windows arealigned with the optical position sensors 40 to enable proper lightdetection from the tracking elements.

The flexible section 903 is formed of highly flexible, transparent filmor foil such as polyethylene film. The rigid sections 908 are formed ofa plastic sheet that is rigid relative to the flexible section 903 andis transparent. The flexible section 903 defines cutouts that receivethe rigid sections 908. The rigid sections 908 are fixed to the flexiblesection 903 in the cutout by, for example, bonding, adhesive, tape, etc.

The engagement of the mounts 904 and magnets 906 provides tactileconfirmation that the drape 902 is properly positioned relative to thecamera unit 936.

With reference to FIGS. 21, 22, and 22A, a tenth embodiment of a cameraand drape assembly 1000 positions a drape 1002 on a casing 1038 of thecamera unit 1036.

The drape 1002 includes a flexible section 1003, i.e., a first section1003, and rigid sections 1006, i.e., second sections 1006. The rigidsections 1006 provide windows 1010 through which light emitted by thetracking elements can be received by the optical sensors 40. The rigidsections 1006 are spaced from one another and separated by the flexiblesection 1003. The rigid sections 1006 are fixed to the flexible section1003.

Bases 1004 are fixed to and extend from the casing 1038 peripherallyabout the optical position sensors 40. The rigid sections 1006 areconfigured to engage the bases 1004 by acting as covers for the bases1004.

First coupling devices 1008 are coupled to the bases 1004. The drape1002 includes second coupling devices 1012 for coupling to the firstcoupling devices 1008. In the embodiment shown, the first couplingdevices 1008 are clamps 1008 (or latches) and the second couplingdevices are protrusions 1012 that act as a catch for the clamps 1008.The clamps 1008 and the protrusions 1012 are configured to releasablylock to each other. In the embodiment shown, the clamps 1008 areconfigured to pivot relative to the bases 1004 to engage detent pockets(not numbered) in the protrusions 1012 on the rigid sections 1006. Morespecifically, the clamps 1008 are fixed to pivot shafts (not numbered)supported in projections on the bases 1004 (see FIG. 22A). The clamps1008 are thereby capable of pivoting about their pivot shafts intoengagement with the detent pockets in the protrusions 1012.

The rigid sections 1006 each include a transparent planar section thatdefines the window 1010 aligned with the optical position sensors 40when the rigid sections 1006 are engaged with the bases 1004. Theengagement of the rigid sections 1006 with the bases 1004 positions thedrape 1002 relative to the camera unit 1036 and supports the drape 1002on the camera unit 1036. The rigid sections 1006 also include aperipheral wall 1011 that depends downwardly from the window 1010 and issized to fit about an upper rim of the bases 1004 when the rigidsections 1006 are mounted to the bases 1004. The windows 1010 may beintegrally formed with the peripheral wall 1011 or may be separate (asshown) and fixed to the peripheral wall 1011 by adhesive, bonding,ultrasonic welding, or other methods.

In the embodiment shown, the flexible section 1003 of the drape 1002 isfixed to the peripheral wall 1011 such that part of the peripheral wall1011, including the portion with the protrusions 1012, extends below theflexible section 1003. As a result, the clamps 1008 are able to engagethe protrusions 1012 by pivoting over the protrusions 1012 and frictionfitting into place without pinching the flexible section 1003therebetween. Detent pockets on the protrusions 1012 facilitate thisengagement, as shown in FIG. 22A. In other embodiments, the rigidsections 1006 may be fixed to the flexible section 1003 such that theperipheral wall 1011, including the protrusions 1012, at least partlyextends above the flexible section 1003 so that the clamps 1008 engagethe protrusions 1012 through the flexible section 1003.

The flexible section 1003 is formed of high flexible, transparent filmor foil such as polyethylene film. The rigid sections 1006 are formed ofa plastic that is rigid relative to the flexible section 1003. Theentire rigid section 1006 may be transparent or only the windows 1010may be transparent. The flexible section 1003 defines cutouts thatreceive the rigid sections 1006. The rigid sections 1006 are fixed tothe flexible section 1003 in the cutouts by, for example, bonding,adhesive, tape, etc.

The engagement of the rigid sections 1006 with the bases 1004 providestactile confirmation that the drape 1002 is properly positioned relativeto the camera unit 1036. The rigid sections 1006 can include coloredborders to identify the portion of the rigid sections 1006 that engagethe bases 1004. The engagement of the clamps 1008 to the protrusions1012 ensures that the windows 1010 remain in alignment with the opticalsensors 40.

With reference to FIGS. 23, 24, and 24A, an eleventh embodiment of acamera and drape assembly 1100 positions a drape 1102 on a casing 1138of the camera unit 1136. The drape 1102 includes a flexible section1103, i.e., a first section 1103, and rigid sections 1106, i.e., secondsections 1106. The rigid sections 1106 provide windows 1108 throughwhich light emitted by the tracking elements can be received by theoptical sensors 40. The rigid sections 1106 are spaced from one anotherand separated by the flexible section 1103. The rigid sections 1106 arefixed to the flexible section 1103.

Bases 1104 are fixed to and extend from the casing 1138 peripherallyabout the optical position sensors 40. The rigid sections 1106 areconfigured to engage the bases 1104 by acting as covers or caps for thebases 1004. In this embodiment, the bases 1104 are first couplingdevices fixed to and extending from the outer casing 1138circumferentially about the optical position sensors 40.

The rigid sections 1106 are configured to engage the bases 1104 toposition the drape 1102 relative to the camera unit 1136 and to supportthe drape 1102 on the camera unit 1136. The rigid sections 1106 includea downwardly extending cap wall 1110 that defines a recess to receiverims of the bases 1104. In this embodiment, the cap walls 1110 aresecond coupling devices 1110 configured to couple to the bases 1104. Thebases 1104 are configured such that the rigid sections 1106 are retainedon the bases 1104 by a friction fit between the bases and the cap walls1110.

The rigid sections 1106 each include a transparent planar section thatdefines the window 1108. Each of the windows 1108 is fixed to one of thecap walls 1110. The windows 1108 may be integrally formed with the capwalls 1110 or may be separate (as shown) and fixed to the cap walls 1110by adhesive, bonding, ultrasonic welding, or other methods. The windows1108 are aligned with the optical position sensors 40 when the rigidsections 1106 are engaged with the bases 1104. The engagement of therigid sections 1106 with the bases 1104 positions the drape 1102relative to the camera unit 1136 and supports the drape 1102 on thecamera unit 1136.

The flexible section 1103 of the drape 1102 is formed of highlyflexible, transparent film or foil such as polyethylene film. The rigidsections 1106 are formed of a plastic that is rigid relative to theflexible section 1103. The entire rigid section 1106 may be transparentor only the windows 1108 may be transparent. The flexible section 1103defines cutouts that receive the rigid sections 1106. The rigid sections1106 are fixed to the flexible section 1103 in the cutouts by, forexample, bonding, adhesive, tape, etc.

The engagement of the rigid sections 1106 with the bases 1104 providesvisual and tactile confirmation that the drape 1102 is properlypositioned relative to the camera unit 1136.

With reference to FIGS. 25, 26, and 26A, a twelfth embodiment of acamera and drape assembly 1200 positions a drape 1202 on a casing 1238of the camera unit 1236. The drape 1202 includes a flexible section1203, i.e., a first section 1203, and rigid sections 1205, i.e., secondsections 1205. The rigid sections 1205 provide windows 1206 throughwhich light emitted by the tracking elements can be received by theoptical sensors 40. The rigid sections 1205 are spaced from one anotherand separated by the flexible section 1203. The rigid sections 1205 arefixed to the flexible section 1203.

Bases 1204 are fixed to and extend from the casing 1238 peripherallyabout the optical position sensors 40. The rigid sections 1205 areconfigured to engage the bases 1204 by acting as covers or caps for thebases 1204. Specifically, the bases 1204 and the rigid sections 1205 areconfigured to friction fit or snap-fit to each other.

The rigid sections 1205 include a transparent top that defines thewindow 1206 and transparent sides extending from the transparent top toa peripheral rim 1208. The rim 1208 is configured to engage the base1204 in a friction fit. The bases 1204 include mating peripheralchannels 1211. The channels 1211 and rims 1208 are the first and secondcoupling devices 1211, 1208 in this embodiment. The rims 1208 areretained in the channels 1211 by an interlocking friction fit. Theengagement of the rigid sections 1205 with the bases 1204 positions thedrape 1202 relative to the camera unit 1236 and supports the drape 1202on the camera unit 1236.

The flexible section 1203 is formed of highly flexible, transparent filmor foil such as polyethylene film. The rigid sections 1205 are formed ofa plastic that is rigid relative to the flexible section 1203. Theflexible section 1203 defines cutouts that receive the rigid sections1205. The rigid sections 1205 are fixed to the flexible section 1203 inthe cutouts by, for example, bonding, adhesive, tape, etc. The flexiblesection 1203 may be attached to the rigid sections 1205 above the rims1208 (as shown in FIG. 26A) so that the rims 1208 are able to engage thechannels 1211 without pinching the flexible section 1203 therebetween.In this case, the flexible section 1203 is attached to the top or sidesof the rigid sections 1205 by bonding, adhesive, tape, etc.

The engagement of the rigid sections 1205 with the bases 1204 providesvisual and tactile confirmation that the drape 1202 is properlypositioned relative to the camera unit 1236. The rigid sections 1205 caninclude colored borders to identify the portion of the rigid sections1205 that engage the bases 1204.

With reference to FIGS. 27-28, a thirteenth embodiment of a camera anddrape assembly 1300 positions a drape 1302 on an outer casing 1338 ofthe camera unit 1336. The drape 1302 includes a flexible section 1303,i.e., a first section 1303, and a rigid section 1306, i.e., secondsections 1306. The rigid sections 1306 provide a window through whichlight emitted by the tracking elements can be received by the opticalsensors 40. The rigid section 1306 is fixed to the flexible section1303. In the embodiment shown, the rigid section 1306 has a centerportion and a plurality of wings (four shown) that extend outwardly fromthe center portion. The rigid section 1306 is planar.

First coupling devices 1304 are fixed to the outer casing 1338 of thecamera unit 1336 to engage the drape 1302 to position the drape 1302relative to the camera unit 1336 and support the drape 1302 on thecamera unit 1336. In this embodiment, the first coupling devices areretainers in the form of hooks 1304.

Elastic bands 1307 are coupled to the rigid section 1306. The elasticbands 1307 engage the hooks 1304 to retain, and position, the rigidsection 1306 over and across the optical sensors 40. The rigid section1306 covers the optical position sensors 40 when the elastic bands 1307are engaged with the hooks 1304. The engagement of the elastic bands1307 with the hooks 1304 provide visual and tactile confirmation thatthe drape 1302 is properly positioned relative to the camera unit 1336.

The flexible section 1303 is formed of highly flexible, transparent filmor foil such as polyethylene film. The rigid section 1306 is formed of aplastic sheet that is rigid relative to the flexible section 1303 and istransparent. The flexible section 1303 defines a cutout that receivesthe rigid section 1306. The rigid section 1306 is fixed to the flexiblesection 1303 in the cutout by, for example, bonding, adhesive, tape,etc. The elastic bands 1307 are fixed to a bottom surface of the rigidsection 1306 beneath the flexible section 1303 so that the elastic bands1307 are able to engage the hooks 1304 without trapping the flexiblesection 1303 therebetween.

The camera units 36, 236, 336, 436, 536, 636, 736, 836, 936, 1036, 1136,1236, 1336 disclosed herein are all similarly configured to communicatewith tracking elements such as the LEDs 50 to determine the positionand/or orientation of objects in the operating room. Each of the cameraunits 36, 236, 336, 436, 536, 636, 736, 836, 936, 1036, 1136, 1236, 1336include a plurality of the optical sensors 40 supported by their casingsand exposed through their casings for detecting the tracking elements.Each of the camera units 36, 236, 336, 436, 536, 636, 736, 836, 936,1036, 1136, 1236, 1336 includes the camera controller 42 incommunication with the optical sensors 40 to receive signals from theoptical sensors 40.

It should be appreciated that features associated with the differentembodiments disclosed herein could be combined in other embodiments. Itshould also be appreciated that the drapes 102, 202, 302, 402, 502, 602,702, 802, 902, 1002, 1102, 1202, 1302 are provided sterile such as byconventional sterilization methods to be used in the operating room toseparate the camera units 36, 236, 336, 436, 536, 636, 736, 836, 936,1036, 1136, 1236, 1336 from the sterile field.

Several embodiments have been discussed in the foregoing description.However, the embodiments discussed herein are not intended to beexhaustive or limit the invention to any particular form. Theterminology which has been used is intended to be in the nature of wordsof description rather than of limitation. Many modifications andvariations are possible in light of the above teachings and theinvention may be practiced otherwise than as specifically described.

What is claimed is:
 1. A camera and drape assembly for use with atracking element of a surgical system, said camera and drape assemblycomprising: a camera unit including a casing and a plurality of opticalsensors supported by said casing for detecting the tracking element; anda drape including a flexible section and a plurality of windows that arerigid relative to said flexible section and surrounded by said flexiblesection, said windows being planar and generally rectangular; whereinsaid camera unit further includes a plurality of first coupling devicesdisposed peripherally about said optical sensors and said drape includesa plurality of second coupling devices for coupling to said firstcoupling devices to align said windows over said optical sensors so thatsaid optical sensors are capable of receiving light from the trackingelement through said windows.
 2. The camera and drape assembly of claim1, wherein said second coupling devices are configured to providetactile confirmation that said drape is properly positioned relative tosaid camera unit when said second coupling devices are coupled to saidfirst coupling devices.
 3. The camera and drape assembly of claim 1,wherein said first coupling devices and said second coupling devices areconfigured to engage each other in a snap-fit connection.
 4. The cameraand drape assembly of claim 1, wherein said windows are transparent. 5.The camera and drape assembly of claim 1, wherein said first couplingdevices and said second coupling devices are generally rectangular. 6.The camera and drape assembly of claim 1, wherein said plurality offirst coupling devices include a plurality of walls disposed about saidoptical sensors and said windows are arranged to abut said walls whensaid second coupling devices are coupled to said first coupling devices.7. The camera and drape assembly of claim 1, wherein said plurality ofsecond coupling devices include a plurality of peripheral walls withsaid windows being separate from and fixed to said peripheral walls. 8.The camera and drape assembly of claim 1, wherein said second couplingdevices include a plurality of colored borders.
 9. A surgical drape foruse with a camera unit having a casing, a plurality of optical sensorssupported by the casing, and a plurality of first coupling devices, saidsurgical drape comprising: a flexible section and a plurality of windowsthat are rigid relative to said flexible section and surrounded by saidflexible section, said windows being planar and generally rectangular;and a plurality of second coupling devices configured to couple to saidfirst coupling devices to align said windows over the optical sensors sothat the optical sensors are capable of receiving light from a trackingelement through said windows.
 10. The surgical drape of claim 9, whereinsaid second coupling devices are configured to provide tactileconfirmation that the surgical drape is properly positioned relative tothe camera unit when said second coupling devices are coupled to thefirst coupling devices.
 11. The surgical drape of claim 9, wherein saidsecond coupling devices are configured to engage the first couplingdevices in a snap-fit connection.
 12. The surgical drape of claim 9,wherein said windows are transparent.
 13. The surgical drape of claim 9,wherein said second coupling devices are generally rectangular.
 14. Thesurgical drape of claim 9, wherein said windows are arranged to abut aplurality of walls of the first coupling devices when said secondcoupling devices are coupled to the first coupling devices.
 15. Thesurgical drape of claim 9, wherein said plurality of second couplingdevices include a plurality of peripheral walls with said windows beingseparate from and fixed to said peripheral walls.
 16. The surgical drapeof claim 9, wherein said second coupling devices include a plurality ofcolored borders.